1. Technical Field
The present invention relates to a vehicle safety apparatus and, in particular, to an inflator for an inflatable vehicle occupant protection device, such as an air bag.
2. Description of the Prior Art
It is known to inflate a vehicle occupant protection device, such as an air bag, to help protect a vehicle occupant. The air bag is inflated by inflation fluid from an inflator. One common type of inflator uses a pyrotechnic material which, when ignited, generates inflation fluid in the form of gas under pressure to inflate the air bag. The air bag is inflated into a position between the vehicle occupant and a portion of the vehicle to help protect the vehicle occupant in the event of a vehicle collision or of an impact to the vehicle.
It is known to tailor the output pressure of the inflator, in order to inflate an air bag in a predetermined manner over a period of time. For example, it is known to begin inflating an air bag at first with inflation fluid at a relatively low pressure, then finish inflating the air bag with inflation fluid at a relatively high pressure. Some known inflators of this type have two actuatable pyrotechnic charges and a separate initiator for each stage. In such an inflator, vehicle electric circuitry separately controls actuation of the two stages of the inflator in response to one or more sensed conditions.